Polymerization of conjugated dienes



Patented Apr. 17, 1945 2,313,753 ronrmzmzarrou or conwcnnn DIENES Charles F. Fryling, Silver Lake, Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Application July 5, 1941,

Serial No. 401,226

13 Claims.

In a copending application of Charles F. Fryling (Serial No. 334,382, filed May 10, 1940) it is pointed out that the polymerization in aqueous emulsion of a monomeric material essentially containing a butadiene is greatly improved when the polymerization is effected in the presence of a free higher fatty acid such as myristic or palmitic acid. The preferred method of conducting the polymerization, according to this copending applica-' tion, is to emulsify the monomeric material with an aqueou emulsifying solution containing both an alkali metal salt of a higher fatty acid and a free higher fatty acid, the emulsifying solution being prepared by partially neutralizing a higher fatty acid with an aqueous alkali solution, the monomeric materials being emulsified in the solution so prepared and then being polymerized.

This application is a continuation-in-part of the above-designated copending application and relates to improvements in the emulsion polymerization process, particularly in-the nature of the emulsifying solution employed.

I have now discovered that the time required for conducting emulsio polymerizations of conj ugated dienes and particularly the time required for such polymerizations to start, that is the insolution one or more free fatty acids together with the fatty acid salts.

The term fatty acid".as used herein is employed in its usually accepted sense to designate those members of both the saturated'and unsaturated aliphatic monocarboxylic acid series such as the CnHmOz, CnHZn-202, and C7lH2n-402 series reduction period, is shortened and that the quality of the polymerization products is improved when at least two alkali metal salts of fatty acids, at least one of which is an alkali salt of a higher fatty acid having emulsifying properties are employed in the preparation of the emulsion. These surprising results are obtained even when there is present only one alkali salt of a higher fatty acid which is an emulsifying agent, the remaining alkali salts being salts of lower fatty acids which are not emulsifying agents, and even when the total amount of fatty acid salts employed is no larger than the amount of emulsifying agent heretofore used.

Accordingly this invention comprises polymerizing a conjugated diene or a monomeric mixture containing a conjugated diene in the presence of a minimum of two alkali salts of fatty acids at least one of which is an alkali salt of a higher fatty acid. In the practice of the invention the various fatty acid salts are employed in the formation of an emulsion of the monomeric materials in water. This is accomplished most advantageously by dissolving the fatty acid salts in water to form an emulsifying solution and tlien mixing the monomer or monomers with the emulsifying solution to form an aqueous emulson which is then polymerized. As will be hereinafter pointed out it is also desirable to include in the emulsifying gardless of the" number of carbon atoms present while the term higher fatty acid is restricted to those fatty acids containing at least 10 carbon atoms. Accordingly, the emulsifying solution may consist of an aqueous solution of an alkali metal salt of a higher fatty acid such as the sodium or potassium salts of such higher saturated fatty acids, as capric, undecylic, lauric, tridecylic, myristic, pentadecylic, palmitic, margaric, stearic, arachidic, behenic or lignoceric acid or the like or of such higher unsaturated fatty acids as undecylenic, duodecylenic, palmitoleic, oleic, linoleic, linolenic, 'hydnocarpic or 'chaulmoogric acid or, the like in admixture with one or more alkali metal salts of any of the above mentioned higher fatty acids or of any other fatty acid such as formic, acetic, propionic, butyric, isobutyric, valeric, isovaleric, caproic, caprylic, pelargonic, crotonic or tiglic or the like. The emulsifying solution may consist solely of a mixture of alkali metal salts of fatty acids in aqueous solution, in which case the fatty acids are referred to as being completely neutralized or it may also contain one or more of the fatty acids in the free state, in which case the fatty acid is spoken of as being only partially neutralized. The emulsifying solutions which have been found to give best results are those containing two or more partially neutralized saturated fatty acids, at least one of which is a higher saturated fatty acid. Specifically, an

aqueous solution containing a mixture of myristic or palmitic acid with one or more other fatty acids having less than ten carbon atoms, and a sufiicient amount of alkali partially to neutralize these fatty acids is preferred. 7

The preparation of the emulsifying solution may be carried out in a number of difierent ways. For example, a mixture of fatty acids may be dispersed in water and the alkali salts of these acids formed by adding an aqueous solution of sodium or potassium hydroxide. The amount of the alkali added may be varied so as to produce a mixture of acids which is neutralized to any desired extent. Again, the emulsifying solution may be prepared by making up separate solutions of fatty acids be present in the emulsifying solution, still another method of preparing such a solution would'be to add the free fatty acid or acids to an aqueous solution of the fatty acid salts.

The concentration of the fatty acidsalts and free fatty acids in the aqueous emulsifying solution may be varied over a wide range but, in general, there should be present from 1 to 5% of fatty acids either completely or partially neutralized. Variation outside this preferred range however is permissible. The pH of the emulsifying solution will obviously depend upon the particular acids employed and their extent of neutralization and will in all cases be somewhat above pH'Z. The most desirable'pH for the emulsion during polymerization has been found to be from about 7.5 to 10, hence the emulsifying solution used in preparing the emulsion to be polymerized should be of this same pH range.

The emulsifying solutions hereinabove described may be employed in the preparation of aqueous emulsions of any monomeric material consisting wholly or in part of a conjugated diene. Thus, the monomeric material may be a butadiene by which is meant butadiene-1,3 or its homologsand analogs such as isoprene, 1,3-dimethyl butadiene-1,3, piperylene, chloroprene and the like, by itself, a mixture of such conjugated dienes or a mixture containing one or more of such dienes and one or more other unsaturated compounds copolymerizable therewith. Such other unsaturated compounds, called comonomers, are in general unsaturated organic compounds containing the polymerizable structure where at least one of the disengaged or unattached valencies is connected to an electro-aetive group, that is a group which substantially increases the electrical dissemetry or polar character of the compound. Among such comonomers there may be mentioned aryl olefins such as styrene, vinyl naphthalene and their chloro or alkoxy substituted derivatives; alpha methylene carboxylic acids and their esters, nitrlles, amides and the like such as acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl methacrylate, methyl ethacrylate, butyl acrylate, isobutyl methacrylate, acrylonitrile, methacrylonitrile, ethacrylonitrile, acryl amide, methacryl amide and the like and other unsaturated comonomers such as vinylidene chloride, methyl vinyl ether, methyl vinyl ketone, vinyl acetate, isobutylene,vinyl acetylene, vinyl ethinyl ethyl carbinol, and various other unsaturated hydrocarbons, esters, ketones, acids, ethers, alcohols and the like. Although the emulsifying solutions of this invention are useful for forming polymerizable aqueous emulsions of any conjugated diene or any monomer mixture containing a conjugated diene, they are especially useful in the formation of emulsions in which the monomeric material consists predominantly of a butadiene since the polymerization of such emulsions produces a synthetic rubber-like material.

As mentioned hereinabove, the practice of this invention involves the emulsiflcation of the monomeric material with the emulsifying solution to form an aqueous emulsion and the polymerization of the emulsion so formed. 'In order for the emulsion to be polymerized most rapidly and efficiently it is often desirable to include in the emulsion certain other substances which influsystems disclosed in copcnding applications of- William D. St: vart, Serial NOS. 379,712 to 379,717,

filed February 14, 1941, (3) polymerization modifiers or regulators such as dialkyl dixanthogens, diaryl disulfides and other organic compounds which increase the solubility and plasticity of polymers formed in their presence and (4) other substances added for some special purpose such as substances which prevent gel formation during the polymerization or perform some other useful function. These other substances may be added to the emulsifying solution or to the monomeric materials before emulsiflcation or to the aqueou emulsion after emulsiflcation as desired.

After the aqueous emulsion containing the various ingredients is prepared, it is then polymerized. This is accomplished by agitating the emulsion at a temperature of about 20 to 50 C. for about 10' to 100 hours. The polymerized emulsion is a latex-like mass which may be coagulated in the usual way to yield the polymeric material.

The method of practicing this invention and the beneficial results obtained by carrying out polymerizations in aqueous emulsions prepared with the novel emulsifying solutions herein disclosed may be illustrated by the following examples. The parts are by weight.

Example 1 A monomeric mixture of parts of butadiene and 25 parts of acrylonitrile are emulsified with 250 parts of an aqueous emulsifying solution containing 1% by weight of myristic acid 1% by weight of lauric acid and sufficient alkali partially to neutralizethe acids and to bring the solution to a pH of 9.6. After the addition of .35 part of hydrogen peroxide as a polymerization initiator, 0.30 part of a polymerization modifier and 0.25 part of a polymerization accelerator, the emulsion thus preparedis agitated in a sealed tube at a temperature of 30 C. After only a 1 hour induction period the polymerization has started and is complete in 16 hours. When the same example is repeated excep that the emulsifying solution contains only in tic acid neutralized, the induction period is 9yhours and the polymerization is only 53% complete in 16% hours. The rubber-like polymer obtained in the first example is also superior to the polymer obtained when only partially neutralized myristic acid is present in the emulsifying solution in that it is more plastic, more coherent and yields vulcanizates having higher tensile strength and elongation.

In the following examples, Example 1 is repeated using emulsifying solutions containing myristic acid, an additional fatty acid and suflicient sodium hydroxide partially to neutralize the acids and to bring the solution to a pH of about 9.6. As in Example 1, 250 c. c. of the emulsifying solution containing 1% by weight of each of the fatty acids is employed for parts of the monomers. In all these examples the presence of the additional fatty acid lowers the induction period and increases the rate of polymerization.

Example No. Additional fatty acid g figg Hours Acetic 2 Isobutync 2 Isovaleric 2% n-Coproic. 2 n-Caprylic. 1% Pelurgonlc. 2

Capric 1% Undecylic 1% 'lridecylie 1 Palmitic Steuric 8 Oleic 1% Undccylenic 1% V The results of these examples are to be compared with an induction period of 9 hours when 2% by weight of only one fatty acid, myristic acid, was used in the preparation of the emulsifying solution. It is significant to note that the replacement of half of the myristic acid, whose alkali salts are the best emulsifying agents of all the fatty acid salts, with such lower fatty acids as acetic, isobutyric and the like which do not form emulsifying agents with alkali, does not hinder the polymerization but actually improves the rate of the reaction. This enables the cost of polymerization to be materially reduced since the relatively expensive myristic acid may be replaced in part by more inexpensive lower fatty acids.

Example A mixture of butadiene and acrylonitrile is polymerized in aqueous emulsion as in Example 1, the emulsifying solution consisting of 250 cc. of an aqueous solution containing 1% by weight of myristic acid, 0.7 by weight of sodium formate and sufficient sodium hydroxide to convert 85%of the myristic acid to sodium myristate. Polymerization begins after an induction period of only 1 hours and is substantially complete in 27 hours. The polymer formed is softer and more plastic than the polymer prepared in the absence of sodium formate. This example shows the improvement in the polymerization brought about by substituting a part of the myristic acid with sodium formate and again illustrates that great economic savings may be effected by the practice of this invention while at the same time the polymerization process is improved.

Example 16 Example 1 is repeated except that the emulsifying solution consists of 250 cc. of an aqueous solution containing 1 by weight of palmitic acid 1% by weight of capric acid and sufllcient sodium hydroxide to neutralize 85% of the fatty acids. The induction period is only 2 hours whereas the induction period required with 85% neutralized palmitic acid alone is 8 hours and that required with sodium caprate alone is 20 hours.

The above examples show that a decrease in induction period, an increase in polymerization velocity, an improvement in polymer properties and a saving in the cost of materials may be effected by carrying out polymerizations in aqueous emulsions containing two or more alkali metal salts of term emulsifying solution is used to designate the aqueous solution containing the various alkali salts of the fatty acids and the Various fatty acids themselves. It is to be understood however that this terminology is used for convenience only and is not meant to impose any restriction on the function of the fatty acid salts or of the free fatty acids when these are employed in emulsion polymerization. It is obvious that some ingredient of the so-called emulsifying solution," probably the alkali metal salt of the higher fatty acid, is responsible for the emulsiflcation or solubilization of the monomeric materials with the water to form whatis called an aqueous emulsion. However certain other ingredients which may be present in the emulsifying solution such as alkali salts of lower fatty acids and free fatty acids are not capable of functioning as emulsifying agents when employed alone and it is probable that their function in this invention when employed in conjunction with an alkali metal salt of a higher fatty acid in polymerization is a catalytic one and is not related to the emulsiflcation. Accordingly in its broadest sense this invention contemplates the polymerization of conjugated dienes in aqueous emulsions containing such fatty acid salts and fatty acids as have been described herein regardless of their function.

Many variations and modifications in this invention are possible and will occur to one skilled in the art. Accordingly it is not intended that the invention be limited except by the spirit and scope of the appended claims.

I claim:

1. The process which comprises polymerizing a monomeric material essentially containing a. conjugated butadiene in an aqueous emulsion containing at least two alkali metal salts of fatty acids at least one of which is an alkali metal salt of a higher fatty acid, said salts being present in fatty acids at least one of which is an alkali metal a concentration less than that which coagulates the emulsion.

2. The process which comprises polymerizing a monomeric material essentially containing a conjugated butadiene in an aqueous emulsion containing at least two alkali metal salts of fatty acids at least one of which is an alkali metal salt of a higher fatty acid and at least one free fatty acid, said salts and said acid being present in a concentration less than that which coagulates the emulsion.

3. The process which comprises emulsifying a monomeric mixture containing a conjugated butadiene and at least one other unsaturated-compound copolymerizable therewith in aqueous emulsion with an aqueous emulsifying solution containing at least two alkali metal salts of fatty acids at least one of which is an alkalimetal salt of a higher fatty acid, said salts being present in a concentration less than that which coagulates the emulsion, and polymerizing the aqueous emulsion thus formed.

4. The process which comprises emulsifying a monomeric mixture containing a. conjugated butadiene and at least one other unsaturated compound copolymerizable therewith in aqueous emulsion, with an aqueous emulsifying solution containing an alkali metal salt of a higher fatty acid having at least ten carbon atoms and at least one alkali metal salt of another fatty acid having less than ten carbon atoms, said last-mentioned salt being present in a concentration less than that which coagulates the emulsion, and polymerizing the aqueous emulsion thus formed.

5. The process which comprises emulsifm'ng a containing an alkali metal salt of a higher saturated fatty acid having at least ten carbon atoms and at least one alkali metal salt of another saturated fatty acid having less than ten carbon atoms, said last-mentioned salt being present in a concentration less than that which coagulates the emulsion, and polymerizing the aqueous emulsion thus formed.

6. The process which comprises emulsifying a monomeric mixture containing a conJugated butadiene and at least one other unsaturated compound copolymerizable therewith in. aqueous emulsion, with an aqueous emulsifying solution containing a higher fatty acid which is partially neutralized with an alkali metal hydroxide and at least one other alkali metal salt of afatty acid, said salt being present in a concentration less than that which coagulates the emulsion, and polymerizing the aqueous emulsion thus formed.

7. The process which comprises emulsifying a, monomeric mixture containing a conjugated butadiene and at least one other unsaturated compound copolymerizable therewith in aqueous emulsion, with an aqueous emulsifying solution containing a mixture of at least two fatty acids, atleast one of which is a higher fatty acid and all of which are partially neutralized wtih an alkali metal hydroxide, said acids and partially neutralized acids being present in a concentration less than that which coagulates the emulsion, and polymerizing the aqueous emulsion thus formed.

8. The process which comprises emulsifying a monomeric mixture of butadiene-1,3 and acrylonitrile with an aqueous emulsifying solution containing at least two alkali metal salts of fatty acids one of which is an alkali metal salt of myristic acid, said salts being present in a concentration less than that which coagulates the emulsion, and

\ polymerizing the aqueous emulsion thus formed.

9. The process which comprises emulsifying a monomeric mixture containing a conjugated bumonomeric mixture of butadiene-L3 and acrylonitrile with an aqueous emulsifying solution containing sodium myristate and at least one other alkali metal salt of a fatty acid having less than ten carbon atoms, said salt being present in a concentration less than that which coagulates the emulsion, and polymerizing the aqueous emulsion thus formed.

10. The process which comprises emulsifying a monomeric mixtureof butadiene-1,3 and acrylonitrile with an aqueous emulsifying solution,

containing myristic acid partially neutralized with an alkali metal hydroxide and at least one other alkali metal salt of a fatty acid, said salt being present in a concentration less than that which coagulates the emulsion, and polymerizing the aqueous emulsion thus formed.

11. The process which comprises emulsifying a monomeric mixture of butadiene-1,3 and acrylonitrile with an aqueous emulsifying solution containing sodium acetate in a concentration less than that which coagulates the emulsion and myristic acid partially neutralized with sodium hydroxide, and polymerizing the aqueous emulsion thus formed.

12. The process which comprises emulsifying a monomeric mixture of butadiene-1,3 and acrylonitrile with an aqueous emulsifying solution containing a mixture of at least two fatty acids one of which is myristic acid and all of which are partially neutralized with an alkali metal hydroxide, said acids and partiallyneutralized acids being present in a concentration less than that "which coagulates the emulsion, and polymerizing the aqueous emulsion thus formed.

13. The process which comprises emulsifying a monomeric mixture of butadiene-1,3 and acrylonitrile with an aqueous emulsifying solution containing myristic acid and lauric acid both of which are from -90% neutralized with an alkali metal hydroxide, and polymerizing theaqueous emulsion thus formed.

CHARLES F. FRYLLNG. 

